Three American physicists have received the Nobel Prize in physics for their contributions to the discovery of gravitational waves.
This could have been an exciting day for Albert Einstein — were he alive, of course. The Nobel Prize in physics for 2017 has been awarded to three researchers for their work helping to prove a prediction he made more than 100 years ago, based on his general theory of relativity: the existence of gravitational waves.
Rainer Weiss (MIT), Kip S. Thorne (Caltech), and Barry C. Barish (Caltech) have been chosen by the Royal Swedish Academy of Sciences for the award thanks to their decisive contributions in the development of the Laser Interferometer Gravitational-Wave Observatory (LIGO) and their observations of gravitational waves.
LIGO consists of two L-shaped laser interferometers, each four kilometers in length, located on opposite sides of the United States. When a gravitational wave — a ripple in spacetime produced by an accelerating mass — reaches the instrument, the wobble it creates in the dimensions of spacetime itself produces minuscule variations (on the order of 10-18 meter, or a million trillionth of a meter) in the length of the interferometer. LIGO measures these tiny stretches and squeezes with its extremely sensitive instruments.
The prize has been awarded to Weiss, Thorne, and Barish, but it’s an acknowledgement of the efforts of roughly 1,000 participants of a project that has been almost 50 years in the works, since Weiss first came up with the idea of an interferometer for detecting gravitational waves. After developing a prototype at MIT in the early 1970s, Weiss teamed up in 1976 with Caltech physicist Kip Thorne, who was instrumental in developing physicists’ understanding of gravitational waves.
In 1979 they started working with Scottish experimentalist Ronald Drever (1931–2017) and together founded the LIGO project. Drever, who added key improvements to Weiss’s detector design, might have been the third recipient of this Nobel, if not for his death this year. Barish came onboard as principal investigator after the project started, becoming science director in 1997. He oversaw critical stages of LIGO’s construction and contributed to securing funding for the project.
The Revolution of Gravitational Waves
LIGO’s first detection of gravitational waves happened in September 2015, after years of tuning and refining the instrument. Three more detections came afterwards, the last one announced just a few days ago on September 27th. The latest discovery included observations from the Advanced Virgo detector of the European Gravitational Observatory near Pisa, Italy, which enabled researchers to pinpoint the location of the waves’ source in the sky with much better precision than previously possible.
All four detections so far appear to come from the merger of stellar-mass black holes, objects with the mass of dozens of Suns contained within a couple hundred kilometers, which is less than the distance between Boston and New York. These objects do not emit any kind of electromagnetic radiation. Before LIGO, astrophysicists didn’t know that black holes existed at these masses, or even that they could come in pairs, Weiss said in a press conference a few hours after the award announcement. Weiss also said that many (including him) thought that LIGO would detect neutron stars first, mostly because astronomers already knew they existed in binaries—which made them a better justification to get funding, he joked.
Although LIGO has not yet announced any detection of neutron star mergers, Weiss hinted an announcement may be coming on October 16th (so brace yourselves for more gravitational wave hubbub very soon).
Gravitational waves open an entirely unexplored route for scientists, like developing an entirely new sense to feel their way around. “With these instruments we have opened a new field of astronomy and astrophysics, so the real payoff will be in the future,” Weiss said. “This [gravitational-wave] radiation is caused by accelerating mases and is so penetrating that nothing perturbs its travel to Earth at all, so it will allow us to see new things and look to what we already know in a new way.”
Scientists hope that gravitational waves will bring new insights to many longstanding questions in astrophysics and cosmology. Questions such as how stiff matter is at its most extreme pressures to how heavy elements are made, how black holes and pulsars rotate over long periods of time — and not only when they smash —and even studying the imprint of the inflationary epoch of the universe
The field of gravitational astronomy is just starting, and we are posed to see very exciting developments in the near future. New ground and space-based instruments are already planned and under construction. The Kamioka Gravitational-Wave Detector is being built in Japan, and it will use extremely cold temperatures to reach high levels of sensitivity. In India, another interferometer will join the LIGO and Virgo collaboration, implementing a spare instrument built by the LIGO team. Finally, the first space-based gravitational wave detector, LISA, is scheduled to launch in 2030 by the European Space Agency and NASA.
The future looks bright for gravitational astronomy.